Abstract in another language

Searching for new technologies, that make solar radiation energy technically usable, the field of organic semiconductors has developed in the last decades in addition to the established inorganic photovoltaics. Both the basic processes involved in charge carrier dissociation in the active layer of the solar cell and questions concerning the morphology of the donor-acceptor interface are still unanswered. However, a targeted further development on the way to new efficient and long-term stable organic solar cells requires an understanding of the elementary separation, recombination and interfacial mechanisms.
Accordingly, the dissociation and recombination of charge carriers in organic donor-acceptor solar cells is investigated in this thesis. Another topic of the study presented here is fullerene diffusion, which decisively influences interface surface morphology and long-term stability. This work focuses on systems made of low-bandgap polymers of the PCDTBT family as donor and fullerenes such as C60 or PCBM as acceptor materials. These systems are analyzed on two levels. At a first level, basic dissociation and recombination mechanisms are investigated. At the center of attention are (i) the intrinsic separation in the donor or acceptor, (ii) the extrinsic separation at the donor-acceptor interface, and (iii) the charge carrier recombination as an important loss process in organic solar cells. In this context, the influence of the quantum energy of the excitation light on delocalization and dissociation of excited states on the donor and the acceptor or on charge-transfer (CT) states at the donor-acceptor interface is taken into account. The influence of light intensity as well as donor layer thickness are also considered. On a second level, processes are investigated which influence the interface morphology of donor and acceptor and thus the separation and recombination mechanisms. In this more "macroscopic" study, the fullerene diffusion or crystallization in a matrix of organic semiconductors is investigated. It contains methods to quantify the fullerene diffusion spectroscopically and to control it by polymer crosslinking. Applying these methods, it is investigated how the long-term stability of the morphology of organic blend solar cells can be improved. Furthermore, it is explored how the concept of multilayer systems can be implemented on the basis of solution-processed polymers.